The present invention relates to an improved scanning control apparatus and method therefor which are applied for an optical character reader or a facsimile device in which a ledger or a document are scanned to obtain picture signals.
Various scanning methods have been developed for optical character readers or facsimile devices. Among of them, a method using a line scanner which comprises a charge coupled device (hereinafter referred to as a CCD) is conventionally known.
In this type of scanning, a main scanning of a ledger or a document is performed by sampling an output from a line scanner in a predetermined period, and a sub-scanning thereof is performed by feeding the ledger or document in a direction perpendicular to the line scanner to obtain picture signals.
Since the sub-scanning is performed by a mechanical operation such as feeding the ledger or the document, a certain time is required for achieving a stable sub-scanning after the start of scanning because of mechanical inertia. FIG. 1 shows a time-feeding distance characteristic of the feeding mechanism in which abscissa and ordinate represent time and feeding distance, respectively.
In FIG. 1, T represents the time that is required for the feeding mechanism to reach a constant velocity. As seen from the figure, the feeding distance per unit time is not constant in the time range of 0 to T.
Therefore, in a prior-art scanning control, the distance between the scanning lines is not uniform in the time range of 0 to T, thereby considerably lowering the quality of the picture signals.